1. Field of the Invention
The present invention relates to a method of heating a film, a method of producing a piezoelectric film and a piezoelectric element, a liquid droplet discharge head, a liquid droplet discharge device, and a light irradiation device.
2. Description of the Related Art
An electric furnace and a Rapid Thermal Annealing (RTA) device have been used for a process of heating a film that is formed on a substrate. In the process, the film is heated to be a temperature that is greater than or equal to a predetermined temperature for a fixed time period. In such a heating process, not only the film, but also the whole substrate is heated.
Some conditions may be imposed for heating the whole substrate. For example, a heat resistant substrate may be required. When another structure and/or an element is disposed on the substrate, a member other than the substrate (e.g., the other structure and/or the element) is also heated, despite that the heating process may not be required for such a member. In such a case, deviation of dimensional precision may be caused, for example, by thermal damage or thermal stress, and performance of the film may be significantly degraded.
As for a silicon device, a heating process by laser irradiation may be applied so as to form a polycrystalline silicon film of a solar cell, or so as to activate a foreign material in an ion implantation layer in a power device, for example. In such a heating process by laser irradiation, a laser beam is directly irradiated onto an object to be heated, so that energy is absorbed by the object. The object is molten once, and subsequently the object is recrystallized. The heating process by laser irradiation may be applied for such a purpose.
The heating process by laser irradiation may be applied for producing an oxide piezoelectric film (e.g., the PZT film). For example, Non-Patent Document 1 (“Highly textured laser annealed Pb(Zr0.52Ti0.48)O3 thin films,” Applied Physics Letters, 99, 042903 (2011)) discloses that a PZT film in an amorphous state, which is formed by a sputtering method, is crystallized by irradiation of a KrF excimer pulsed laser beam.
Furthermore, for example, Non-Patent Document 2 (“Ferroelectric properties of Lead Zirconate Titanate thin film on glass substrate crystallized by continuous-wave green laser annealing,” Japanese Journal of Applied Physics, 49, 04DH14 (2010)) discloses that a heating process of 350° C. is applied to a PZT film that is formed by a sol-gel method on a quartz substrate having a platinum electrode and a titanium layer. Subsequently, a continuous-wave green laser beam having a wavelength of 532 nm is irradiated onto a surface side (i.e., the side on which the PZT film is formed) of the quartz substrate, and the PZT film is crystallized by heating the platinum electrode.